Active matrix/organic light-emitting diode (AMOLED) display device is currently one of the hotspots in the field of flat-panel display devices. The OLED has such advantages as low power consumption, low production cost, self-luminescence, wide viewing angle and rapid response. As a core technique for the AMOLED display device, the design of a pixel driving circuit is of an important significance. For the AMOLED display device, a stable current is required so as to control the OLED to emit light.
As shown in FIG. 1, an existing typical AMOLED pixel driving circuit includes one driving transistor DTFT, one switching transistor T1 and one storage capacitor Cs. When one row of scanning lines is selected, a scanning signal Gate(n) on this row is of a low level, T1 is turned on, and a data voltage Vdata corresponding a grayscale level is written into the storage capacitor Cs. After this row of scanning lines has been scanned, Gate(n) is changed to be of a high level, T1 is turned off, and DTFT is driven by a gate voltage stored in Cs, so that a current is generated by DTFT to drive the OLED, thereby to ensure the OLED to emit light continuously within one frame. The current IOLED flowing through the OLED=K(VGS−Vth)2=K(Vdata−ELVDD−Vth)2, wherein K is a constant, VGS is a gate-to-source voltage of DTFT, Vth is a threshold voltage of DTFT, and ELVDD is a power supply voltage. An existing pixel compensation circuit merely compensates for the drift of the threshold voltage Vth of DTFT in each pixel generated due to the manufacture process and the aging of elements.
However, it should be appreciated that, as can be seen from the above equation for calculating the current flowing through the OLED, the current is also affected by the power supply voltage ELVDD. Because the OLED is a current-driven element, there is a relatively large current flowing through a power line for applying the power supply voltage ELVDD. As shown in FIG. 2, on an OLED display panel, the pixels in each column within an effective display region are connected to a corresponding power line, and the power supply voltage is applied by a power supply lead ELVDD_O located outside the effective display region to the power lines within the effective display region. The large current flows through, from top down, the power lines within the effective display region, so on the OLED display panel, the power supply voltage ELVDD at an upper left portion is larger than that at a middle left portion, and the power supply voltage ELVDD at the middle left portion is larger than that at a bottom left portion. Identically, the power supply voltage ELVDD at an upper right portion is larger than that at a middle right portion, and the power supply voltage ELVDD at the middle right portion is larger than that at a bottom right portion.
In FIG. 2, a first power supply voltage input point BLP is located on the OLED display panel at the bottom left, a second power supply voltage input point ULP is located on the OLED display panel at the upper left, a third power supply voltage input point URP is located on the OLED display panel at the upper right, a fourth power supply voltage input point BRP is located on the OLED display panel at the bottom right, a fifth power supply voltage input point MLP is located on the OLED display panel at the middle left, and a sixth power supply voltage input point MRP is located on the OLED display panel at the middle right. VULP>VMLP>VBLP, VURP>VMRP>VBRP, wherein VULP is a voltage at ULP, VMLP is a voltage at MLP, VBLP is a voltage at BLP, VURP is a voltage at URP, VMRP is a voltage at MRP, and VBRP is a voltage at BRP.
As can be seen from the above equation for calculating the current flowing through the OLED, the brightness of the entire OLED display panel gradually increases from top down, i.e., the brightness unevenness occurs. In the related art, an appropriate material is selected so as to reduce a resistance of the power line for applying the ELVDD, thereby to reduce a difference in an IR drop (which refers to a voltage drop or rise across a network in an existing integrated circuit (IC) between the power supply and the ground). However, along with an increase in the resolution, there is less room for the power lines, and as a result, the IR drop become very serious on the OLED display panel.